feat(key_binder): bind key to a key sequence Closes #301
feat(key_binder): bind key to a key sequence
Closes #301

To bind a key to a key sequence,
set 'send_sequence' attribute of a 'key_binder/bindings' entry.

Special named keys should be around with "{" and "}".
Notice that you have to add quotes when writing a filed with "{" or "}" in a
yaml file.

For example:
key_binder:
  bindings:
    - { when: composing, accept: a, send_sequence: aa }
    - { when: composing, accept: Right, send_sequence: "{Right}{Right}" }
    - { when: composing, accept: Left, send_sequence: "aa{Left}{Left}" }

rime/librime,rime/librime,rime/librime,rime/librime